The three gods and the goddess whose names are thus commemorated in the days of the week hold also a prominent place among the Scandinavian deities, where they appear under the names of Ty (_Týr_), Odin (_Óðinn_), Thor (_þórr_), and Frigg. But while Odin and Thor actually hold the place which they might be expected to occupy as objects of worship, the warlike deity Ty has apparently become of secondary importance. This is indicated not only by the native Scandinavian evidence, but also by what can be gleaned from external sources. In an Old English sermon[1] by the Abbot Ælfric, about the year 1000, the mention of some of the Roman deities leads the preacher to introduce the corresponding Danish names. Jove or Jupiter, he says, 'was called Thor among some peoples, and him the Danes love most of all.' Mercury, too, 'was honoured among all the heathens, and he is otherwise called Othon in Danish.' Of Ty there is no mention, although Mars is one of the Roman deities specified by name. In another homily by Ælfric there is the same identification of Thor and Odin, along with 'the foul goddess Venus, whom men call Frigg,' but here also Ty is ignored.
More than merely negative evidence, however, is supplied by another outside source, which is the leading contemporary account of Scandinavian religion, viz. that given by the German historian, Adam of Bremen (about the year 1075), in his description of the great temple of the Swedes at Upsala, and of the gods worshipped there. Here he writes, 'the people venerate the statues of three gods, so placed that the most powerful of them, Thor, has his seat in the middle of the bench. On either side of him Wodan and Fricco have their places. Of these the significations are as follows. Thor, they say, presides in the air, and governs thunder and lightning, winds and rains, fair weather and crops. The next, Wodan, that is "Fury," carries on wars and gives men valour against their enemies. The third is Fricco, bestowing peace and pleasure upon mortals.' The image of Wodan, he adds, resembled that of the Roman Mars; that of Thor suggested Jupiter, while Fricco was represented in a form resembling the minor deity Priapus.
The god here called Fricco was known to the Scandinavians themselves by the name of Frey (_Freyr_), and that the triad thus specified by Adam were in fact the chief deities worshipped in the later stages of Scandinavian religion is abundantly proved by the native evidence. The identification of Odin with Mars in place of Mercury is also in full accordance with the later beliefs: in other words, Odin has taken the place of Ty as the chief war-god. Whether this was the main reason for the admission of Frey as third member of the supreme triad is uncertain, the earlier position of this god being altogether unknown. Thor, it will be noticed, still retains his place as the counterpart of the Roman Jupiter, and stands between the other two gods, as being the most powerful. The precise relationship, however, between Thor and Odin is not by any means so simple as this statement would suggest, and forms indeed one of the most difficult questions connected with the subject. This will be most clearly brought out by a detailed account of the relative place assigned to each of them in religious practice on the one hand, and in mythological accounts on the other; and the most correct impression of the facts will probably be obtained by dealing first with Thor.